My wife and I bought our first home last year. Originally when looking for a home, a large Southern Live Oak tree in the front yard was on our short list of things we really wanted in a house. However, the housing market began changing rapidly and we had to act fast. We were unable to get our tree. We plan on staying in our home for many years, so why not plant one? I've been looking at 3"-5" caliper trees and my only (major) concern is the relative location to the septic tank and drain field. I recently acquired the building plans to my home so I know exactly where these are located. Looking around the web, I've heard everything from "Go for it, just dump *insert chemical here* into your toilet..." to "DON'T DO IT!" We really want this tree, but we need help! Can we plant this tree? If not this one, perhaps another type of shade tree?

How close is relatively close. You might talk to an old septic tank pumper to get real life experience or tree farm manager or county extension agent.
The place you would like the tree may not be the best location because of septic field. Septic problems are never fun or cheap. Be flexible and heed knowledgeable advise.
I do know stay away from willows and silver maples near septic and sewers.

Any tree planted will seek water and nutrients. Most will invade the leech field if planted to close and can completely clog the lines. They even invade sewer lines, that is what keeps Roto Rooter in business.

We have established oak trees near our septic system. The septic system was installed @ 10 years ago in order to meet new septic laws - required when a house is sold. They cleared a lot of trees in order to install the system. So the trees that we have now were there when they installed the system. I would say that the trees are closer to the tank than the field. The sites that I have seen definitely don't recommend planting trees on the leaching field. You may find this site helpful.http://inspectapedia.com/septic/Plant_Trees_Over_Septic_Fields.htm

IF (and that's a big if) the septic tank and interconnecting lines are properly sealed and leak free you should be able to plant trees near them -- with limits. As a general rule of thumb the root zone of a tree roughly matches the canopy, though some species have larger root zones than canopies. So if a tree has a 20' diameter canopy it will also have a 20' diameter root zone. If the root zone encroaches into the area of the septic tank the roots can damage the tank even if it's not leaking; though smaller roots are less likely to cause damage than larger roots. In most cases the pipes will be OK but if the root is large enough it can damage a pipe, too. It's the same reasons not to plant large trees close to the house: the roots can damage the foundation.

So your homework is to find out how big the tree will be at maturity and, more specifically, how large its root zone will be. If the tank and pipes are at the fringes of the root zone you will probably be OK.

Under no circumstances should you plant a tree whose roots can encroach into the leach field. Once they reach that nice, fertile water, they will grow cancerous-like to plug up the leach field.

Live oaks love water and will find the septic lines in time- it's just a question of how long unless you're talking a hundred feet distance- then you may be OK. And at the end of the lines is better than closer in. Moving the septic system may be a (costly) option too. I love oaks too but mature ones aren't going to happen in what's left of my lifetime so I go to them instead of planting- I can't wait on their schedule!